Magnetron



Sept. I3, 1938.

MAGNETRON Filed July 1 1937 H. E. HOLLMANN 2 Sheets-Sheet 1 INVENTOR f/ANS'ER/CHHOLLMANN BY I ATTORNEY Sept. 13, 1938. H. E. HOLLMANN MAGNETRON 2 Sheets-Sheet 2 Filed July 1, 1957 INVENTOR HANS ER/C'f/HOLLMANN ATTORNEY Patented Sept. 13, 1 938 MAGNETRON Hans Erich Hollmann, Berlin, Germany, assignor to Telefunken Gesellschaft fiir Drahtlose Telegraphic 111. b. H., Berlin, Germany, a corporation of Germany Application July 1, 1937, Serial No. 151,412 In Germany July 16, 1936 5 Claims.

My invention relates to electron discharge devices, more particularly to. such devices employing a magnetic field for influencing the movement of the electrons within the device.

- The present invention has for its principal object circuit arrangements, the purpose of which are to stabilize as far as possible the operating point of a magnetron, i. e., a tube having a hot.- cathode in which the electron movements are influenced by a magnetic field, and also to render such a tube independent of and unaffected by accidental fluctuations of operating conditions such as the anode potential, tube heating, etc;

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims, but the invention itself will best be understood by reference to the following description taken in connection with the accompanying drawings in which Figure 1 is a graph showing the characteristics of a device of the type under consideration, Figure 2 shows a discharge device and circuit made according to my invention, Figures 3 and 4 are graphs of the operating characteristics of the discharge device and circuit shown in Figure 2, Figure 5 shows a 25 modification of a discharge device and circuit made according to my invention, Figure 6 shows a discharge device and circuit particularly suitable for a transmitter and made according to my invention, Figure '7 shows the characteristic of a discharge device used as an oscillator, and Figure 8 shows another circuit arrangement and discharge device made according to my invention.

It is known in the prior art that the anode current of a simple two-electrode tube or diode if traversed by a magnetic flux, suddenly droops as soon as a certain critical magnetic field intensity Hk has been attained (see Figure 1). Plotting the anode current I9. against the current Im, there result the well known magnetron characteristics. The latter are shifted in a way as shown in Figure 1 for various parameters, i. e., anode poten-' tials Ea- The critical field intensity H1; becomes so much greater, the higher Ea because the deflection of electrons of higher velocity requires stronger magnetic forces. In this simple form, the magnetron is adapted to widely varying purposes, for instance, for the generation, amplification, and reception of electrical oscillations.

Now, such a comparatively steep drop of the magnetron characteristics requires an extremely careful and delicate adjustment of the neutral or quiescent operating point to suit various practical objects. For reception of electrical waves, the working point must be chosen in the-upper or lower knee of the magnetron characteristic, in order to amplify or produce oscillations in the linear part thereof. In order that the adjustment of the operating point once chosen may be stabilized and preserved for fairly prolonged periods of operation, exactly stable and constant working conditions are required, above all, constant heating, a constant anode potential, and a constant magnetic field, inasmuch as even the slightest fluctuations of the three factors referred to immediately cause a shift of the working point through the drooping part of the magnetron characteristic and thus render the magnetron inoperative.

In order that a certain improvement may be insured in this regard, that is to say, in order to make the working adjustment of a magnetron less affected by and liable to disturbing variations of the three factors above enumerated, one plan would be to utilize the anode current for exciting the magnetic field. This could be accomplisha-ble by causing the same to traverse the field windings or else by deriving the exciting current from the anode potential. In both these methods, the magnetic field intensity would be raised whenever the heating or the anode voltage increases, and this would counteract a rise of current in the magnetron occasioned by both changes by virtue of the fact that the operating point upon the new magnetron characteristic is shifted downwards again. In this manner, undesirable fluctuations of the working conditions are capable of being compensatedonly to a certain degree, in fact, the compensatory action is not adequate to insure stabilization that will satisfy all practical requirements.

Now, it is here where the present invention provides a substantial improvement in that the field excitation is made to be a function both of the discharge current as well as of the anode potential, with the consequencethat a compound effect is obtained. To this end, the field winding of the exciting magnet for the tube M, having cathode K and anode P as shown in Figure 2, is divided into two solenoids or coils S1 and S2. Of these the latter is included in the circuit of the magnetron tube and is traversed by the anode current Ia or a current proportional to the anode current, while the former S1 is fed directly from the anode potential source of supply Ea. In order that the working points may be chosen most favorably, and in order that the compound or combination action may be divided in a definite manner between the two coils, regulating resistances Wrand W2 are provided. These may acteristics at operating points A to A.

be connected either in parallel or in series with the field coils according to the practical requirements. In order that, moreover, the operating point where the compound windings start to become operative may be determined, there could further be provided a third magnetic field component which is independent of the operating conditions of the magnetron. For this object,

either'the core of the exciting magnet is made permanently magnetic, or else a third field coil S3 is provided which is fed with an energizing current which is independent of Ea and Ia.

The operation of this compound excitation is explained in more detail by' reference to Figures 3 and 4. First solenoid S2, which is dependent upon the anode current, will be examined. Figure 3 shows two distinct magnetron characteris tics which distinguish themselves by different emission currents Ie'Ie" as parameters, and which, in the presence of constant anode potential are obtainable most simply by adjustment of the cathode heating. Coil S1 thus furnishes a constant magneticfield component H1 which fixes on the abscissa axis a definite starting point for the action of S2. The field component furnished from S2 is proportional to the product of number of turns and current, hence, it may be represented in the diagram by a straight line which has an angle of inclination or slope corresponding to the number of turns and which starts at the end of H1. If both coils S1 and S2 comprise the same number of turns, then in lieu of the magnetic field intensity, the magnetizing current may be plotted on the abscissa axis seeing that the other magnetic conditions are identical for the two solenoids. It can be seen from the diagram that the straight magnetizing line for emission current Ie intersects the corresponding magnetron characteristic at the working point A which on changing to characteristic Ie' is shifted but very little to A.

In order to appraise the effect of the second magnetic field component H1 due to the anode potential when the same is variable, it is necessary to revert to the family of curves already shown in Figure 1, that is to say, to difierent magnetron characteristics, with constant saturation current Is and anode potentials Ea to Ea as parameters, this family of curves being shown once. more in Figure 4. In order to facilitate an examination and to render the situation as lucid as possible,

the case shall be assumed where the field com.- I

,ponent H1 is equal to the critical magnetic field intensity Hk. Inasmuch as the magnetron char.- acteristics experience a parallel shift proportional to Ea, i. e., when E9. is raised, and since then also H1 grows in direct proportion tO.Ea, this implies that the ends of the various field components Hi to H1 will always lie upon the abscissa axis at a point where the anode current begins to droop. Now, from these points must be plotted the straight field lines characterizing winding S2, for a constant angle of inclination or slope, and these will intersect the various magnetron char- It will be seen that it is thus feasible to fix all of the working points at a definite point of the magnetron characteristic.

The compound winding of a magnetron field magnet is useful not only when the magnetron is doing transmitter work where inadvertent and unintended fluctuations of the operating conditions tending to impair the efliciency must. be compensated, but also where the magnetron. op.- erates as a receiverfor ultra-short waves. In

this case, as is known from the art, the operating point must be fixed at the lower or upper knee or bend of the characteristic, although the working conditions, for other reasons, must be capable of wide variation. For it will be understood that maximum sensitivity of reception, for magnetron type receivers, will in the first place be realized when the electron transit times (electron oscillation periods) inside the tube are tuned to the incoming signal wave, and, in the second place, when the receiver is close to the self-oscillating point, a point which may most easily be attained by variation of the heating of the tube. In this instance, tuning of the anode voltage and regulation of regeneration through heating may be insured without it being necessary to pay particular attention to the stabilization of the proper operating point seeing that this is secured by the action of the compound winding.

What is also to be noted is that the effect of the compound winding should affect only slow variations, but should not affect variations due to the demodulation or modulation currents. Since here mostly relatively high frequencies are involved, the desired state will alone be insured, to a certain degree, even by the inductance of the windings S1 and S2; otherwise the time-constant must be correspondingly raised by connecting in parallel sufiiciently large capacitors.

Another improvement of the working conditions is obtained by regulating the exciting current for the magnetic field through a .control tube with the anode current. By the amplifying action peculiar to the control tube particularly precise. stabilization is insurable.

Figure 5 shows a circuit scheme comprising a control tube in which due regard has been given to the magnetron tube itself, whereas all circuit elements serving for amplification or oscillation have been omitted for the sake of greater clarity of illustration because these details are in no casual relationship to the invention. Referring to Figure 5, M denotes the magnetron tube in the plate or anode circuit of which is included the resistance W between the cathode K and the negative pole of the anode voltage source of supply Ea. R designates the regulator tube controlling the magnetic field whose plate current flows through winding F of the field magnet. For energizing the tube including the magnetic winding F the anode potential Ea may be employed. In this manner linking of the field excitation and the anode potential Ea is directly obtained. Another relation with the magnetron current is assured through the resistance W which furnishes the. grid voltage for the regulator or control tube R. For instance, if the anode potential grows, this results in an increase both of the magnetron current Ia as well as of the anode current of tube R and the magnetizing current Im, with the result that the working point of the magnetron characteristic is shifted in downward directionwith av tendency to restore the original state. Moreover, the increase in the current in the'magnetron through the intermediary of resistance W renders the grid of the control tube more positive and the magnetic field is still further reinforced. The total ensuing stabilizing and regulator action is extremely eflicient. The action of the regulator'tube R will be of a corresponding nature whenever the current variations of the magnetron are ascribable to fluctuations in the heating or emission or RF actions no matter of what origin or nature. For in all instances, the action of the magnetic field will coun- 7 teract variations of current in the magnetron by causing a corresponding shift of the working point.

However, the regulator effect hereinbefore described will operate in phase, in other words, in the sense of stabilization, only as long as the static magnetron characteristics are uniform. This is not always the case, indeed, the most serious distortions will arise when the magnetron serves as a wave generator for ultra-short waves either with a cylindrical anode closed upon itself or with an anode cylinder split two or more times into a corresponding number of segments.

Such a magnetron transmitter comprising an oscillatory system L interposed between the anode segments is illustrated in Figure 6. As a consequence of the dynamic electron transmits or oscillations which are occasioned by the action of the radial anode field and the transverse ma netic field, and which will come to be in resonance with the radio frequency potentials arising between the anode segments, the static Ia-Im characteristics of the entire oscillator are not smooth curves or uniform but have dips in the curves, and these tend to turn the stabilizing steps and means hereinbefore disclosed into the opposite; in other words, the adjustment of the working point is rendered unstable rather than stable. Under this condition, the use of a distinct regulator or control tube affords a simple chance to reverse the phase of regulation by the magnetron current simply by transposing the connecting leads between the regulating resistance W and grid and filament of tube R in a way as indicated in Fig ure 6. If, then, the working point experiences a shift as a result, say, of radio frequency tuning or energy-abstraction actions, for instance, in the direction of growing magnetron current, the grid of the regulator tube will become more negative, and the magnetic field is weakened. If, then, the static magnetron characteristic as a consequence assumes a shape as shown in Figure '7, the working point may be located upon the rising branch b-c, and this is advantageous for modulation work. In this case the drooping branches of the graph a,b and dc are unstable so that when connecting the transmitter, the magnetron characteristic will change from a through b to the working point A.

If the magnetron tube is fitted with terminal plates designed to shut the anode cylinder at both ends and which collect the escaping electrons, then also the electronic current flowing to these terminal plates may be utilized at the same time for regulation of the magnetic field. This is accomplished by including resistance W not in the anode circuit, but rather in the terminal plate circuit, and by taking the grid potential for the regulator tube therefrom. Also in this instance, by proper choice of the connecting leads of grid and cathode according to- Figures 5 and 6 any desired phase may be adjusted for regulation as shown, for instance, in the circuit arrangement Figure 8.

The circuit organizations hereinbefore disclosed stabilize the operating point at arbitrarily adjustable places of the magnetron characteristic, and this is required in a great many practical cases, for example, when the magnetron is to be modulated by variations of the anode potential. Now, in order that stabilization under these circumstances may affect really only the working point and not by chance also the modulation variations (in which latter case they would suppress and wipe out the entire modulator action) care must be taken sothat stabilization occurs with a certain time-constant. In most practical cases, the inductance inherent in the magnetrange of the magnetron characteristic, but only the region which is really concerned in such control action, another field winding F could be provided in addition to the field winding F fed from the regulator tube R, as shown in Figure 8. This second field winding could be directly fed with anode potential Ea as shown in this exemplified embodiment. Other auxiliaries beside resistance W designed to adjust the desired stabilizing action and the desired working point are shunt or series resistances connected to F or a variable grid bias potential for the regulator tube, though not all of these details are indicated in the circuit diagrams.

It is a known fact that the operation of a magnetron is afunction not only of the intensity, but also of the direction of the magnetic field traversing the discharge space. As a general rule, it is advantageous to orientate field so that it presents a small angle of inclination with reference to the axis of the electrode system. This end is accomplished not only by rotation of the magnet or of the tube itself, but it may be effected also by forming the magnetic field of two componental fields presenting a slope with reference to each other, for instance, by placing these field components .at right angles to each other, while the intensity thereof is so balanced that the resulting field will have the desired intensity and direction. In order to obtain stabilization of the working point by turning the field, it would be feasible to act by ways and means described, upon the intensity of the field component at approximately right angles to the main field parallel to the axis of the system. Inasmuch as this field component is comparatively feeble it follows that the corresponding exciting current is small. Hence, the regulator action is restricted to circuits with lower loads and the same is practicable by the aid-of circuit elements of reduced dimensions. More particularly speaking, a control tube of far-lower power may then be utilized.

While I have indicated the preferred embodiments of my invention of which I am now aware and have also indicated only one specific application for which my invention may be employed, it will be apparent that my invention is by no means limited to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departing from the scope of my invention as set forth in the appended claims.

What I claim as new is- 1. An electron discharge device having a straight thermionic cathode and an anode surrounding said cathode, means for producing a magnetic field parallel to and between said cathode and anode, a source of voltage supply connected to said anode, a second electron discharge device having an anode, cathode, and grid, said means for producing the magnetic field and said second electron discharge device being connected in series across said source of voltage supply, and a resistance connected in series'with the first electron discharge device, the grid and cathode of said second electron discharge device being connected across said resistance.

2. An electron discharge device having a straight thermionic cathode and an anode surrounding said cathode, means for producing a magnetic field parallel to and between said cathode and anode, a source of voltage supply connected to said anode, a second electron discharge device having an anode, cathode, and grid, said means for producing the magnetic field and said second electron discharge device being connected in series across said source of voltage supply, and a resistance connected in series with the first electron discharge device, the grid and cathode of said second electron discharge device being connected across said resistance, the grid of said second electron discharge device being connected between the resistance and said first electron discharge device.

3. An electron discharge device having a straight thermionic cathode and an anode surrounding said cathode, means for producing a magnetic field parallel to and between said cathode and anode, a source of voltage supply connected to said anode, a second electron discharge device having an anode, cathode, and grid, the means for producing the magnetic field and said second electron discharge device being connected in series across said source of voltage supply, and a resistance connected in series with the first electron discharge device, the grid and cathode of said second electron discharge device being connected across said resistance, the cathode of the second electron discharge device being connected between the resistance and said first electron discharge device.

4. An electron discharge device having a straight thermionic cathode and an anode surrounding said cathode, an end member at either end of said anode, means for producing a magnetic field parallel to and between said cathode and anode, a source of voltage supply connected to said cathode and anode, asecond electron discharge device having a cathode, grid, and anode, the means for producing the magnetic field and said second electron discharge device being connected in series across said source of voltage supply, a resistor connected to said end members and to one side of said source of voltage supply, the grid and cathode of said second electron discharge device being connected across said resistor.

- 5. An electron discharge device having a straight thermionic cathode and an anode surrounding said cathode, an end member at either end of said anode, means for producing a magnetic field parallel to and between said cathode and anode, a source of voltage supply connected to said cathode and anode, a second electron discharge device having a cathode, grid, and anode, the means for producing the magnetic field and said second electron discharge device being connected in series across said voltage supply, a resistor connected to said end members 130 and to one side of said source of voltage supply, the grid and cathode of said second electron discharge device being connected across said resistor, a second resistor connected between the grid of said second electron discharge device and between the end members and said first resistor,

and a condenser connected across the grid and cathode of said second electron discharge device.

H. E. HOLLMANN. 

